Aquaculture has commonly been conducted by growing fish, prawns and other marine invertebrates in outdoor ponds. The ponds however eventually become polluted because faeces, uneaten food and algae work their way to the bottom of the ponds. This makes the ponds almost impossible to clean. In addition large quantities of valuable water are required to keep these systems functional. Other disadvantages are also associated with outdoor aquaculture systems. For example pests can eat stock, adverse weather conditions such as floods can cause stock loss by washing the stock away and very hot weather can cause growth of algal blooms which can kill the stock. In addition in very hot or very cold weather, the stock will stop growing. Muddy waters or disturbed water can also cause the stock to have an unpalatable taste.
In order to overcome the above disadvantages, indoor commercial aquaculture systems were introduced where fish or other marine invertebrates are grown in tanks placed in large buildings or sheds. Such systems have a number of advantages. In particular, there is a continuing circulation of the water around the system with the addition of approximately 10 percent of its water volume each week unlike in outdoor ponds where water is pumped in and then overflows back into streams and rivers causing added pollution. In the indoor systems, the water temperature is attempted to be controlled by either heating the water with probes placed into the water or by installing large chillers and pumping the water and through the chillers to cool it to the desired temperature to promote fast fish growth. The temperature control equipment is relatively expensive in capital cost and also running costs can be high. An alternative is to control air temperature, however as the tanks and associated equipment make up less than 20 percent of the air area within the building or shed, to have effective water temperature control, very large energy absorbing equipment would in most cases have to be used. Further, the buildings or sheds would have to be fully insulated to be viable and this would mean an impractical cost in relation to returns.
A further disadvantage of the known systems is that the buildings or sheds housing the aquiculture system resemble a maze of pipes and plumbing as water is pumped between the system components such as tanks, filters, biological filters, foam fractionators, ultraviolet water treatment units and other water treatment components. These components are individual components which have to be set up in different parts of the building. Drainage pipes are provided on the floor and water pipes are connected to each individual tank or component. One of the major problems with these system is that with a large number of pipes interconnecting the components, vibration in the pipes or simply the suspension of pipes can creates stresses causing pipe joints to fail and/or pipe fracture. If such a failure occurs, water from the tanks is quickly lost resulting in the loss of tonnes of fish stock. Further wherein there is a large volume of exposed piping, water temperature losses occur in cold climates and water temperature increases occur in hot climates resulting in massive increases in the electricity costs for cooling or heating the water. This has in many cases made the indoor systems commercially unviable. Another disadvantage which arises is that fish often attempt to jump out of the tanks so additional piping has to be placed over the top of the tanks and then covered with netting to prevent fish losses.
With regards to the individual components, if ultraviolet water treatment units are installed, they are installed into the main water flow pump line which reduces flow thus increasing the electricity consumption. In the foam skimmers or foam fractionators which are used in the conventional systems, insufficient bubbles or foam is created or forced out of the top of the units. If insufficient bubbles or foam is created, the fractionators simply do not function. To make them function correctly, high pressure high energy pumps fitted with air venturis are employed but these do not always overcome the problem of inefficient operation.
Drum filters have been a part of the aquaculture systems for filtering the water of fine waste particles created from waste food, faeces, and other extraneous matter. The majority of filters are electric motor driven off central drive shafts with bearings on which the drum filter is supported for rotation. In most cases the cleaning takes place through a centre mounted vertical disc through which the water must pass. The drum filters are separate units and include an outer housing which is specifically designed to hold the filter and its supporting components and to also hold the water. Water inlets and outlets must also be provided along with special float switches to activate a cleaning process when the water level rises.
As a general rule, during cleaning the water flow is stopped or bypassed which allows uncleaned water back into the fish tanks. If the water is stopped for any length of time, it can be very detrimental to the fish stock as in times of heavy stock loading, the fish can only stay alive for around six minutes before fatalities begin to occur. Another major drawback is that if a bearing or another major mechanical failure happens, removal the drum filter and all of the fittings is extremely time consuming and in many cases can lead to total stock losses. Cleaning of the current drum filters in any event is difficult as easy access cannot be had to the interior of the drum.